At present, in many instances, the surveillance of swimming pools is carried out by human monitoring. This type of monitoring is made difficult because of reflection, refraction, and water agitation, which can make it difficult to identify visually a motionless body at a depth of less than a meter when a lifeguard is not properly positioned.
The risk of drowning in a swimming pool occurs primarily when a bather is not sufficiently capable of swimming, for example in the case of a young child, or when a swimmer succumbs to a medical emergency. In the first case, lifeguards on duty or individuals close to the bather in distress may have their attention attracted by the bather himself, in particular if the bather is momentarily able to flap his arms while trying to stay on the surface. In the second case, however, the swimmer may lose consciousness without attracting attention from lifeguards or nearby swimmers. A bather who is unable to raise his head above water will experience respiratory impairment and then respiratory distress. Without intervention, a bather in respiratory distress will progress to cardiac arrest. Depending on the body structure of the bather in distress and the amount of water inhaled and ingested during the drowning process, a bather who has suffered this type of incident may sink to the bottom of the pool or, less commonly, he may also float unconscious below the surface of the water.
When respiratory impairment begins, which marks the onset of drowning, an experienced lifeguard, in particular skilled in artificial resuscitation, has less than three minutes to give aid to the victim. If proper aid is given within this time, the victim will not generally suffer long-term physiological effects from the incident. In general, if aid is given between three and five minutes after consciousness has been lost, a time which nevertheless varies between individuals, the victim may survive but there is risk of irreversible brain damage. Biological death occurs at the point at which irreversible brain damage begins (4 to 6 minutes without oxygen) and clinical death occurs within minutes thereafter.
Various devices have been proposed to provide assistance to lifeguards in the detection of distressed swimmers/bathers. One such device is disclosed in U.S. Pat. No. 5,043,705, which is directed to the use of sonar for monitoring a swimming pool. According to this device, at least one sonar transmitter/receiver is provided on the bottom of the swimming pool, and a layer is monitored using this equipment. However, a device of this type has a considerable drawback because, in order to install the sonar and connect it to the processing equipment which derives information from the echoes which are received, it is necessary to route cables through the bottom of the swimming pool and below this bottom, which leads to an entirely prohibitive cost if the pool has already been constructed. Moreover, safety rules prohibit the use of voltages in excess of 12 or 24 volts, depending on the country, close to the water in a swimming pool, whereas it is necessary to use voltages of several hundred volts in order to generate sonar pulses. Furthermore, the signal obtained with sonar includes echoes due to the swimming pool walls, and it is extremely difficult to eliminate the noise signal thus obtained in order to make it possible to detect the signal corresponding to the submerged body of a drowning individual. In addition, sonar essentially makes it possible to identify the body of a drowning individual by the volume of air which it contains; if a victim has his lungs filled with water, the signal obtained will not at all conform to what might be expected and may even not be identified by the signal processing. It will therefore be understood that a system of this type cannot be satisfactory.
It has also been proposed, to use cameras working in the visible wavelength range to monitor a swimming pool, these cameras being arranged in such a way that the observed region lies in a volume close to and parallel with the bottom of the swimming pool. In this device, the cameras only observe a layer of water parallel to the bottom, which means that the number of cameras needs to be increased if the bottom is not flat, as well as leaving most of the volume of the swimming pool unmonitored. Furthermore, this device does not make it possible to detect motionless bodies just below the surface of the water. Lastly, the cameras and their accessories are immersed in the swimming pool, which is unacceptable in terms of safety and causes considerable problems in connecting them to the signal processing equipment associated with them. This device cannot therefore be satisfactory.
Other technology based surveillance systems for a swimming pool are known. These systems may include one or numerous control screens which are positioned by the lifeguards' chairs or in the offices of the persons responsible for surveillance of the swimming pool. Alarms may be given through a sound and/or visual warning, in particular with an indication of the zone of the swimming pool in which a suspicious event is taking place.
However, such systems are often not perfect, allowing various significant events to go undetected. For example, it is not always possible to distinguish a shadow of a body of a swimmer passively floating, moving along the bottom, as numerous conditions must be met for the detection systems to work properly. In various systems, it is desirable for the viewpoints to be close to the object being observed. This first condition implies that numerous cameras will be used for surveillance over a large zone in relation to the dimensions of the objects that one hopes to detect. In correlation, this type of system is consequently particularly costly. For optimum use, it is desirable that the depiction of colors perceived by each camera is identical. Consequently, it is essential for the opto-electronic characteristics of the video cameras to be the same, which is not always the case. In addition the optical route between the object and each camera may cross environments with different refraction or transparency indexes. This is notably the case when the body being observed is submerged in a swimming pool with a turbulent surface. The depiction of the colors of the object being observed by each camera is not the same. Consequently the geometric correlations that make it possible to establish that the images (their outlines and grey scale nuances) produced by each camera come from the same dense object situated in front of a colored bottom, cannot be verified with certainty. Consequently, confusion is possible between a shade of color (for example a shadow being carried) on the bottom of the swimming pool and a dense object close to the bottom. Consequently, the result is that errors in detection and false initiation of the alarm systems.
In addition, the installation of complicated technology based systems is not practical in many existing swimming pools. Existing swimming pools may not have the infrastructure to support the installation of the systems. In addition, even if the systems could be installed, the price of installation and operation may be prohibitive.
It would, therefore, be beneficial to provide a method for properly and optimally positioning lifeguard stations around a swimming pool or other body of water to provide the lifeguards with proper views of the entire pool to prevent drowning incidents. In addition, it would be beneficial to provide a method which can be used with existing swimming pools or other bodies of water to minimize drowning incidents without incurring significant installation and maintenance costs.